Multiferroic BiFeO3 thin films have been prepared on Pt/TiO2/SiO2/thick (200 μm) and membrane (15 μm) Si substrate by pulsed laser deposition (PLD) to confirm the influence of stress from substrate. Si membrane was obtained by etching using reactive ion etching (RIE) until thickness is to be 15 μm. The X-ray diffraction peaks of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 μm) membrane substrate slightly shift to lower angles, compared to those on Pt/TiO2/SiO2/Si (200 μm) substrate. Ferroelectric hysteresis loops were also measured at 150 K before and after Si etching by RIE. The BiFeO3 thin film on the Pt/TiO2/SiO2/Si (15 μm) membrane structure shows remanent polarization (Pr ) of 95 μC/cm2 for a maximum applied voltage of 18 V, which is larger than Pr = 71 μC/cm2 of BiFeO3 thin film on Pt/TiO2/SiO2/Si (200 μm) substrate at the same measurement conditions. Under magnetic field of 1.1 T, remanent polarization (Pr) of BiFeO3 thin film on Pt/TiO2/SiO2/Si (15 μm) membrane structure increased from 95 μC/cm2 to 101 μC/cm2 at 150 K due to stress relaxation of BiFeO3 thin film.